Level conversion device and method

ABSTRACT

A device is disclosed and includes a first transistor, a second transistor, and a first current limiter. First terminals of the first and second transistors are coupled to an output terminal, and gate terminals of the first and second transistors receive a first input signal. A first terminal of the first current limiter is coupled to a second terminal of the first transistor to output a first output signal, and a second terminal of the first current limiter is coupled to a second terminal of the second transistor to output a second output signal. A third output signal at the output terminal has a logic value different from that of the first input signal.

RELATED APPLICATIONS

This application is a continuation of the U.S. application Ser. No. 17/005,197, filed Aug. 27, 2020, now U.S. Pat. No. 11,063,578, issued on Jul. 13, 2021, which is a continuation of the U.S. application Ser. No. 16/686,110, filed Nov. 16, 2019, now U.S. Pat. No. 10,778,197, issued on Sep. 15, 2020, which is a continuation of the U.S. application Ser. No. 16/410,886, filed May 13, 2019, now U.S. Pat. No. 10,483,950, issued Nov. 19, 2019, which is a continuation of the U.S. application Ser. No. 16/219,525, filed Dec. 13, 2018, now U.S. Pat. No. 10,291,210, issued on May 14, 2019, which is a continuation of U.S. application Ser. No. 15/851,403, filed Dec. 21, 2017, now U.S. Pat. No. 10,164,615, issued Dec. 25, 2018, which is a continuation of U.S. application Ser. No. 14/942,909, filed Nov. 16, 2015, now U.S. Pat. No. 9,866,205, issued Jan. 9, 2018, all of which are herein incorporated by reference.

BACKGROUND

With rapid development of manufacturing process technology, low power design has been widely utilized in many applications. For example, level shifters are generally used to interface voltage signals between diversely different circuits that operate with different power voltages from each other. However, when operating at a lower power voltage, for example, a sub-threshold voltage, the operations of the level shifter are failed due to leakage currents.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a schematic diagram of a device, in accordance with various embodiments of the present disclosure;

FIG. 2 is a circuit diagram of the device in FIG. 1, in accordance with various embodiments of the present disclosure;

FIG. 3 is a flow chart of operations of the device in FIG. 2 when the input signal VIN has a logic value of 1, in accordance with various embodiments of the present disclosure;

FIG. 4 is a flow chart of operations of the device in FIG. 2 when the input signal VIN has a logic value of 0, in accordance with various embodiments of the present disclosure;

FIG. 5 is a circuit diagram of the device in FIG. 1, in accordance with various embodiments of the present disclosure;

FIG. 6 is a circuit diagram of the device in FIG. 1, in accordance with various embodiments of the present disclosure;

FIG. 7 is a circuit diagram of the device in FIG. 1, in accordance with various embodiments of the present disclosure;

FIG. 8 is a circuit diagram of the device in FIG. 1, in accordance with various embodiments of the present disclosure;

FIG. 9 is a circuit diagram of the device in FIG. 1, in accordance with various embodiments of the present disclosure; and

FIG. 10 is a circuit diagram of the device in FIG. 1, in accordance with various embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

The terms used in this specification generally have their ordinary meanings in the art and in the specific context where each term is used. The use of examples in this specification, including examples of any terms discussed herein, is illustrative only, and in no way limits the scope and meaning of the disclosure or of any exemplified term. Likewise, the present disclosure is not limited to various embodiments given in this specification.

Although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

FIG. 1 is a schematic diagram of a device 100, in accordance with various embodiments of the present disclosure. In some embodiments, the device 100 is implemented in a level converter or as a level converter.

As illustratively shown in FIG. 1, the device 100 includes an input signal generator 120, a level shifter 140, a selector 160, and an output stage 180. For illustration, the input signal generator 120 includes an inverter 120A. The input signal generator 120 is configured to input an input signal VIN, and further output an input signal VINB, by the inverter 120A, in response to the input signal VIN. In other words, in some embodiments, the input signal VIN is an inverse of the input signal VINB. In some embodiments, the input signal VINB is a phase shift of the input signal VIN. In some embodiments, the input signal VINB is generated by a logical or arithmetical operations of the input signal VIN.

The level shifter 140 is configured to adjust the voltage level of the input signal VIN to generate an output signal VO1 and an output signal VO2. For illustration, the maximum voltage of the voltage level of the input signal VIN is set to a voltage VDDI. The level shifter 140 is able to adjust the maximum voltage of the input signal VIN from the voltage VDDI to a voltage VDDO, in which the voltage VDDO is different from the voltage VDDI.

The selector 160 is configured to transmit one of the output signal VO1 and the output signal VO2 to the output stage 180 according to the input signals VIN and VINB. The output stage 180 is configured to adjust the voltage swing of the one of the output signal VO1 and the output signal VO2 transmitted from the selector 160, in order to generate an output signal VO4. In some embodiments, the output stage 180 includes one or more buffers that pull the voltage swing of one of the output signals VO1 and VO2 to full range, to generate the output signal VO4. Effectively, the driving ability of the device 100 is increased by the output stage 180. For illustration, the full range of the voltage swing is configured from a voltage VSS which is, for example, a ground voltage, to the voltage VDDO which is, for example, a power voltage.

In some embodiments, the input signal generator 120 operates with the voltage VDDI, while the level shifter 140, the selector 160, and the output stage 180 operate with the voltage VDDO. In some embodiments, the voltage VDDI is lower than or equal to the voltage VDDO. For example, the voltage VDDI ranges from about 0.2 Volts to about 1.2 Volts, and the voltage ranges VDDO is about 1.2 Volts. Alternatively, in some other embodiments, the voltage VDDI is higher than or equal to the voltage VDDO. For example, the voltage VDDI is about 1.2 Volts, and the voltage VDDO ranges from about 0.2 Volts to about 1.2 Volts. In other words, in some embodiments, the level shifter 140 is able to pull up the voltage level of the input signal VIN to a higher voltage. Alternatively, in some embodiments, the level shifter 140 is able to pull down the voltage level of the input signal VIN to a lower voltage.

The arrangements of the voltage VDDI and the voltage VDDO are given for illustrative purposes. Various arrangements of the voltage VDDI and the voltage VDDO are within the contemplated scope of the present disclosure.

Reference is now made to FIG. 2. FIG. 2 is a circuit diagram of the device 100 in FIG. 1, in accordance with various embodiments of the present disclosure.

In some embodiments, the level shifter 140 includes switches M1-M4 and current limiters 141 and 142. The level shifter 140 generates the output signal VO1 at a first terminal of the current limiter 141, and generates the output signal VO2 at a second terminal of the current limiter 141.

For illustration, a first terminal of the switch M1 is configured to receive the voltage VDDO, a second terminal of the switch M1 is coupled to the first terminal of the current limiter 141, and a control terminal of the switch M1 is coupled to a second terminal of the current limiter 142 and receives a control signal VC. A first terminal of the switch M2 is coupled to the second terminal of the current limiter 141, a second terminal of the switch M2 is configured to receive the voltage VSS, and a control terminal of the switch M2 is configured to receive the input signal VIN. A first terminal of the switch M3 is configured to receive the voltage VDDO, a second terminal of the switch M3 is coupled to a first terminal of the current limiter 142, and a control terminal of the switch M3 is coupled to the second terminal of the current limiter 141 to receive the output signal VO2. A first terminal of the switch M4 is coupled to the second terminal of the current limiter 142, a second terminal of the switch M4 is configured to receive the voltage VSS, and a control terminal of the switch M4 is configured to receive the input signal VINB. In some embodiments, the voltage VSS is lower than the voltage VDDO.

In some embodiments, the switches M1 and M3 operate as pulling-up units of the level shifter 140. For illustration, when the switch M1 is turned on by the control signal VC, the voltage level of the first terminal of the current limiter 141 is thus pulled up to the voltage VDDO through the switch M1. Accordingly, the first terminal of the current limiter 141 generates the output signal VO1 corresponding to the pulled up voltage level. When the switch M3 is turned on by the output signal VO2, the voltage level of the first terminal of the current limiter 142 is pulled up to the voltage VDDO through the switch M3.

Corresponding to the switches M1 and M3, the switches M2 and M4 operate as pulling-down units of the level shifter 140. For illustration, when the switch M2 is turned on by the input signal VIN, the voltage level of the second terminal of the current limiter 141 is pulled down to the voltage VSS through the switch M2. When the switch M4 is turned on by the input signal VINB, the voltage level of the second terminal of the current limiter 142 is pulled down to the voltage VSS. Accordingly, the second terminal of the current limiter 142 generates the control signal VC corresponding to the pulled down voltage level.

With the arrangements for the switches M1-M4, a self-control mechanism is implemented in the level shifter 140. Detailed operations are described below with reference to FIG. 3 and FIG. 4.

In some approaches without using the current limiters 141 and 142, when the input signal VIN is a sub-threshold voltage having, for example, a voltage level of about 0.2 Volts, the switch M1 and the switch M2 are turned on at the same time. In such a condition, if a current IM1 flowing from the switch M1 to the switch M2 is greater than a current IM2 flowing through the switch M2, the pulling-down operation of the switch M2 is failed. Effectively, the operations of the level shifter 140 are failed. Based on the above, the device in these approaches cannot be operated with a sub-threshold voltage.

Compared with the aforementioned approaches, in some embodiments, the current limiter 141 is utilized to reduce the current IM1 flowing from the switch M1 to the switch M2, and the current limiter 142 is utilized to reduce a current IM3 flowing from the switch M3 to the switch M4. Alternatively stated, the current limiter 141 is configured to generate a voltage drop between the switches M1 and M2, in which the voltage drop is sufficient to reduce the current IM1. The current limiter 142 is configured to generate a voltage drop between the switches M3 and M4, in which the voltage drop is sufficient to reduce the current IM3. With such arrangements, the switch M2 is able to pull down the voltage level of the second terminal of the current limiter 141 to the voltage VSS when the input signal VIN is a low voltage, for example, the sub-threshold voltage.

In some embodiments, the current limiter 141 and the current limiter 142 are resistive devices. In various embodiments, the current limiter 141 and the current limiter 142 are diodes. In further embodiments, the diodes for implementing the current limiter 141 and the current limiter 142 are formed with various types of transistors. For illustration, as shown in FIG. 2, the current limiter 141 includes a diode-connected metal-oxide-silicon field-effect transistor (MOSFET) M5, and the current limiter 142 includes a diode-connected MOSFET M6. Effectively, the diode-connected MOSFET M5 provides the voltage drop, i.e., the threshold voltage of the diode-connected MOSFET M5, between the switches M1 and M2. The diode-connected MOSFET M6 also provides a voltage drop, i.e., the threshold voltage of the diode-connected MOSFET M6, between the switches M3 and M4. As a result, the current IM1 flowing toward the switch M2 and the current IM3 flowing toward the switch M4 are reduced.

The configurations of the current limiters 141 and 142 are given for illustrative purposes. Various configurations of the current limiters 141 and 142 are within the contemplated scope of the present disclosure.

With continued reference to FIG. 2, in some embodiments, the selector 160 includes switches M7 and M8. The switch M7 is coupled between the first terminal of the current limiter 141 and the output stage 180. The switch M7 is configured to be turned on according to the input signal VIN, to transmit the output signal VO1 from the first terminal of the current limiter 141 to the output stage 180. The switch M8 is coupled between the second terminal of the current limiter 141 and the output stage 180. The switch M8 is configured to be turned on according to the input signal VIN, to transmit the output signal VO2 from the second terminal of the current limiter 141 to the output stage 180.

Reference is now made to both of FIG. 2 and FIG. 3. FIG. 3 is a flow chart 300 of operations of the device 100 in FIG. 2 when the input signal VIN has a logic value of 1, in accordance with various embodiments of the present disclosure.

In various embodiments, the input signal VIN is able to have a logic value of 1 or 0. As shown in FIG. 3, operations of the device 100 in FIG. 2 are described with respect to the input signal VIN having a logic value of 1.

In operation S310, the switch M2 is turned on by the input signal VIN. In operation S320, the voltage level of the second terminal of the MOSFET M5 is pulled down to the voltage VSS. Accordingly, the output signal VO2 corresponding to the pulled down voltage level of the second terminal of the MOSFET M5 is generated. In operation S330, the switch M8 is turned on by the input signal VIN to transmit the output signal VO2 to the output stage 180. In operation S340, the output stage 180 outputs the output signal VO4 in response to the output signal VO2.

In some embodiments, the voltage swing of the input signals VIN and VINB ranges from the voltage VSS to the voltage VDDI, in which the voltage VSS corresponds to the logic value of 0, and the voltage VDDI corresponds to the logic value of 1. For illustration, as shown in FIG. 2, when the input signal VIN has the logic value of 1, the input signal VINB accordingly has the logic value of 0. The switch M2 is thus turned on by the input signal VIN. Accordingly, the voltage level of the second terminal of the MOSFET M5 is pulled down to the voltage VSS, in order to generate the output signal VO2 having the level of the voltage VSS. The voltage level of the first terminal of the MOSFET M5 is then transited to the voltage VSS+VTH5 through the diode-connected MOSFET M5, in which VTH5 is a threshold voltage of the MOSFET M5. Furthermore, the switch M8 is turned on by the input signal VIN to transmit the output signal VO2 to the output stage 180. The output stage 180 generates the output signal VO4 having the logic value of 1 according to the output signal VO2.

As described above, in the operations S310-S340 illustrated above, the diode-connected MOSFET M5 provides a voltage drop i.e., the threshold voltage of the MOSFET M5, between the switches M1 and M2. In other words, the diode-connected MOSFET M5 effectively operate as a resistive device between the switches M1 and M2, to provide a resistance to reduce the current flowing from the switch M5 to the switch M2, compared to the approaches using no current limiter. With such arrangements, the current IM1 flowing from the switch M1 to the switch M2 is reduced. As a result, the pulling down operation of the switch M2 is able to be performed with a sub-threshold voltage.

Reference is now made to both of FIG. 2 and FIG. 4. FIG. 4 is a flow chart 400 of operations of the device 100 in FIG. 2 when the input signal VIN has the logic value of 0, in accordance with various embodiments of the present disclosure.

Alternatively, as shown in FIG. 4, operations of the device 100 in FIG. 2 are described with the input signal VIN having the logic value of 0. In operation S410, the switch M2 is turned off by the input signal VIN. In operation S420, the switch M4 is turned on by the input signal VINB. In operation S430, the voltage level of the second terminal of the MOSFET M6 is pulled to the voltage VSS, to generate the control signal VC. In operation S440, the switch M1 is turned on by the control signal VC. In operation S450, the voltage level of the first terminal of the MOSFET M5 is pulled up to the voltage VDDO. Accordingly, the output signal VO1 corresponding to the pulled up voltage level of the second terminal of the MOSFET M5 is generated. In operation S460, the switch M7 is turned on by the input signal VIN to transmit the output signal VO1 to the output stage 180. In operation S470, the output stage 180 outputs the output signal VO4 in response to the output signal VO1.

For illustration, as shown in FIG. 2, when the input signal VIN has the logic value of 0, the input signal VINB accordingly has the logic value of 1. The switch M2 is thus turned off by the input signal VIN. The switch M4 is thus turned on by the input signal VINB, to transmit the voltage VSS to the second terminal of the MOSFET M6. Accordingly, the voltage level of the second terminal of the MOSFET M6 is pulled down to the voltage VSS, to generate the control signal VC. The switch M1 is turned on by the control signal VC. Accordingly, the voltage level of the first terminal of the MOSFET M5 is pulled up to the voltage VDDO, to generate the output signal VO1 having the level of the voltage VDDO. The voltage level of the second terminal of the MOSFET M5 is then transited to the voltage VDDO-VTH5. The switch M7 is also turned on by the input signal VIN, to transmit the output signal VO1 to the output stage 180. As a result, the output stage 180 generates the output signal VO4 having the logic value of 0 according to the output signal VO2.

It is noted that, in the operations S410-S470 illustrated above, the diode-connected MOSFET M6 provides a voltage drop, i.e., a threshold voltage of the MOSFET M6, between the switches M3 and M4. In other words, the diode-connected MOSFET M6 effectively operates as a resistive device between the switches M3 and M4, to provide a resistance to reduce the current flowing from the switch M6 to the switch M2. With such arrangement, the current IM3 flowing from the switch M3 to the switch M4 is reduced. As a result, the pulling down operation of the switch M4 is able to be performed with a sub-threshold voltage.

In some embodiments, the operations illustrated in the flow chart 300 in FIG. 3 and the operations illustrated in the flow chart 400 in FIG. 4 are implemented as a level conversion method.

Reference is now made to FIG. 5. FIG. 5 is a circuit diagram of the device 100 in FIG. 1, in accordance with various embodiments of the present disclosure.

Compared with the device 100 in FIG. 2, like elements in FIG. 5 are designated with the same reference numbers for ease of understanding. In some embodiments illustrated in FIG. 5, the input signal generator 120 of the device 100 further includes an NAND gate 120B. An output terminal of the NAND gate 120B is coupled to an input terminal of the inverter 120A. In some embodiments, the NAND gate 120B operates as an enabling unit of the input signal generator 120. For illustration, the NAND gate 120B is configured to receive an initial input signal IN and an enable signal EN, and output the input signal VINB to the inverter 120A according to the initial input signal IN and the enable signal EN. The inverter 120A is further configured to output the input signal VIN according to the input signal VINB.

When the initial input signal IN and the enable signal EN both have the logic value of 1, the input signal VINB has the logic value of 0. Accordingly, the input signal VIN has the logic value of 1. With such arrangements, the level shifter 140 is enabled to perform the level conversion for the input signal VIN, as discussed above, when the enable signal EN has the logic value of 1.

When the initial input signal IN has the logic value of 1 and the enable signal EN has the logic value of 0, the device 100 is disabled. In such a condition, the NAND gate 120B outputs the input signal VINB having the logic value of 1. The inverter 120A then outputs the input signal VIN having the logic value of 0. Accordingly, the switch M7 is turned on by the input signal VIN, to transmit the output signal VO1 having the logic value of 1 to the output stage 180, as discussed above in FIG. 4. As a result, the output stage 180 receives the output signal VO1 having the logic value of 1 and outputs the output signal VO4 having the logic value of 0. In other words, when the device 100 is disabled, the device 100 keeps outputting the output signal VO4 having the logic value of 0, instead of outputting a floating voltage.

In some embodiments, the NAND gate 120B and the inverter 120A operate with the voltage VDDI. In other words, both of the maximum voltage level of the input signals VIN and VINB and the maximum voltage level of the enable signal EN are set to the voltage VDDI.

Reference is now made to FIG. 6. FIG. 6 is a circuit diagram of the device 100 in FIG. 1, in accordance with various embodiments of the present disclosure.

Compared with the device 100 in FIG. 2, like elements in FIG. 6 are designated with the same reference numbers for ease of understanding. In some embodiments illustrated in FIG. 6, the input signal generator 120 of the device 100 further includes an NOR gate 120C. An output terminal of the NOR gate 120C is coupled to an input terminal of the inverter 120A. In some embodiments, the NOR gate 120C operates as an enabling unit of the input signal generator 120. For illustration, the NOR gate 120C is configured to receive the initial input signal IN and an enable signal ENB, and accordingly output the input signal VINB to the inverter 120A. The inverter 120A is configured to output the input signal VIN according to the input signal VINB. In some embodiments, the NOR gate 120C and the inverter 120A operate with the voltage VDDI.

Furthermore, compared with the device 100 in FIG. 5, in some embodiments illustrated in FIG. 6, the device 100 is enabled when the enable signal ENB has the logic value of 0. When the enable signal ENB has the logic value of 1, the NOR gate 120C outputs the input signal VINB having the logic value of 0. The inverter 120A thus generates the input signal VIN having the logic value of 1. As a result, the output stage 180 outputs the output signal VO4 having the logic value of 1. In other words, when the device 100 is disabled, the device 100 keeps outputting the output signal VO4 having the logic value of 1, instead of outputting a floating voltage.

The arrangements of the input signal generator 120 in FIGS. 5-6 are given for illustrative purposes. Various arrangements of the input signal generator 120 are within the contemplated scope of the present disclosure.

Reference is now made to FIG. 7. FIG. 7 is a circuit diagram of the device 100 in FIG. 1, in accordance with various embodiments of the present disclosure.

Compared with the device 100 in FIG. 2, like elements in FIG. 7 are designated with the same reference numbers for ease of understanding. In some embodiments illustrated in FIG. 7, the level shifter 140 further includes a switch M9. A first terminal of the switch M9 is coupled to the second terminals of the switches M2 and M4, a second terminal of the switch M9 is configured to receive the voltage VSS, and a control terminal of the switch M9 is configured to receive the enable signal EN. The switch M9 is configured to be turned on according to the enable signal EN, so as to enable the switches M1-M6. In other words, in some embodiments, the switch M9 operates as an enabling unit of the level shifter 140.

Furthermore, compared with FIG. 2, in some embodiments illustrated in FIG. 7, the output stage 180 of the device 100 includes a buffer 182, a control circuit 184, and a buffer 186. An input terminal of the buffer 182 is coupled to the selector 160 to receive one of the output signal VO1 and the output signal VO2. The buffer 182 then outputs an output signal VO3 according to the one of the output signal VO1 and the output signal VO2. The control circuit 184 is coupled between the buffers 182 and 186. The control circuit 184 is configured to output a buffer signal VB according to the output signal VO3 and the enable signal EN. The buffer 186 is configured to output signal VO4 according to the buffer signal VB. In some embodiments, the control circuit 184 includes an NAND gate 184A. For illustration, as shown in FIG. 7, when the enable signal EN has the logic value of 1, the switch M9 is turned on to enable the switches M1-M6. In such condition, the logic value of the buffer signal VB is determined by the output signal VO3, as discussed above in FIGS. 3-4. When the output signal VO3 has the logic value of 1, the buffer signal VB has the logic value of 0. Alternatively, when the output signal VO3 has the logic value of 0, the buffer signal VB has the logic value of 1. When the enable signal EN has the logic value of 0, the switch M9 is turned off, and the switches M1-M6 are also turned off. Effectively, the level shifter 140 is disabled. In such condition, the NAND gate 184A outputs the buffer signal VB having the logic value of 1. As a result, the buffer 186 accordingly outputs the output level of the logic value of 0. With such arrangements, when the level shifter 140 is disabled, the device 100 keeps outputting the output signal VO4 having the value of 0, instead of outputting a floating voltage.

In some embodiments, the switch M9 and the output stage 180 operate with the voltage VDDO. In other words, the maximum voltage level of the enable signal EN is set to the voltage VDDO.

Reference is now made to FIG. 8. FIG. 8 is a circuit diagram of the device 100 in FIG. 1, in accordance with various embodiments of the present disclosure.

Compared with the device 100 in FIG. 7, like elements in FIG. 8 are designated with the same reference numbers for ease of understanding. In some embodiments illustrated in FIG. 8, the switch M10 of the device 100 is coupled to the switches M1 and M3. In some embodiments, the first terminal of the switch M10 is configured to receive the voltage VDDO, the second terminal of the switch M10 is coupled to both of the first terminals of the switches M1 and M3, and the control terminal of the switch M10 is configured to receive the enable signal ENB. The switch M10 is configured to be turned on according to the enable signal ENB to enable the switches M1-M6. In some embodiments, the enable signal ENB is an inverse of the enable signal EN. For illustration, when the enable signal EN has the value of 1, the enable signal ENB has the value of 0. In such condition, the switch M10 is turned on to enable the switches M1-M6. The logic value of the buffer signal VB is determined according the one of the output signal VO1 and the output signal VO2 transmitted from the level shifter 140. Alternatively, when the enable signal EN has the logic value of 0, the enable signal ENB has the logic value of 1. In such condition, the switch M9 is turned off. Effectively, the level shifter 140 is disabled. As a result, the NAND gate 184A outputs the buffer signal VB having the logic value of 1, and the buffer 186 keeps outputting the output signal VO4 having the logic value of 0.

Reference is now made to FIG. 9. FIG. 9 is a circuit diagram of the device 100 in FIG. 1, in accordance with various embodiments of the present disclosure.

Compared with the device 100 in FIG. 7, like elements in FIG. 9 are designated with the same reference numbers for ease of understanding. In some embodiments illustrated in FIG. 9, the control circuit 184 is coupled to an output terminal of the selector 160 and the buffer 182. The control circuit 184 is configured to transmit the voltage VDDO to the buffer 182 according to the enable signal EN. The buffer 182 is configured to receive one of the output signals VO1 and VO2, and the voltage VDDO, and accordingly output the output signal VO3. The buffer 186 is coupled to the buffer 182 to receive the output signal VO3, and outputs the output signal VO4 in response to the output signal VO3.

In some embodiments, the control circuit 184 includes a switch M11. A first terminal of the switch M11 is configured to receive the voltage VDDO, a second terminal of the switch M11 is coupled to the selector 160 to receive one of the output signals VO1 and VO2, and a control terminal of the switch M11 is configured to receive the enable signal EN. For illustration, when the enable signal has the logic value of 1, the switch M9 is turned on, and the switch M11 is turned off. Accordingly, the switches M1-M6 are enabled. As a result, the logic value of the output signal VO4 is determined according to the input signal VIN, as discussed above in FIGS. 3-4. Alternatively, when the enable signal EN has the logic value of 0, the switch M9 is turned off to disable the switches M1-M6. In such condition, the switch M11 is turned on by the enable signal EN, to transmit the voltage VDDO to the buffer 182. Effectively, the buffer 182 receives a signal having the logic value of 1. As a result, the buffer 186 outputs the output signal VO4 having the logic value of 1. With such arrangements, when the level shifter 140 is disabled, the device 100 keeps outputting the output signal VO4 having the logic value of 1, instead of outputting a floating voltage.

Reference is now made to FIG. 10. FIG. 10 is a circuit diagram of the device 100 in FIG. 1, in accordance with various embodiments of the present disclosure.

Compared to the device 100 in FIG. 8 and FIG. 9, like elements in FIG. 10 are designated with the same reference numbers for ease of understanding. In some embodiments illustrated in FIG. 10, the control circuit 184 is coupled to an output terminal of the selector 160 and the buffer 182. The arrangement of the control circuit 184 in FIG. 10 is same as the arrangement of the control circuit 184 in FIG. 9. Thus, the related descriptions are not repeated here.

For illustration, as shown in FIG. 10, when the enable signal EN has the logic value of 1, the enable signal ENB has the logic value of 0. Accordingly, the switch M10 is turned on by the enable signal ENB, and the switch M11 is turned off by the enable signal EN. As a result, the switches M1-M6 are enabled, and the logic value of the output signal VO4 is determined according to the input signal VIN, as discussed above in FIGS. 3-4. Alternatively, when the enable signal EN has the logic value of 0, the enable signal ENB has the logic value of 1. Accordingly, the switch M10 is turned off by the enable signal ENB to disable the switches M1-M6, and the switch M11 is turned on by the enable signal EN to transmit the voltage VDDO to the buffer 182. As a result, the buffer 186 outputs the output signal VO4 having the logic value of 1.

As described above, the device 100 in the present disclosure is able to convert the sub-threshold voltage to a standard supply voltage for low-voltage circuits and systems. Moreover, the device 100 in the present disclosure is also able to convert the standard supply voltage the sub-threshold voltage according to practical applications. In other words, the device 100 in the present disclosure is able to operate with a wide voltage operation range.

In this document, the term “coupled” may also be termed as “electrically coupled,” and the term “connected” may be termed as “electrically connected”. “Coupled” and “connected” may also be used to indicate that two or more elements cooperate or interact with each other.

In some embodiments, a device is disclosed and includes a first transistor, a second transistor, and a first current limiter. First terminals of the first and second transistors are coupled to an output terminal, and gate terminals of the first and second transistors receive a first input signal. A first terminal of the first current limiter is coupled to a second terminal of the first transistor to output a first output signal, and a second terminal of the first current limiter is coupled to a second terminal of the second transistor to output a second output signal. A third output signal at the output terminal has a logic value different from that of the first input signal.

Also disclosed is a device that includes a level shifter having a first transistor and a second transistor. A gate terminal of the first transistor receives a first input signal, and a gate terminal of the second transistor receives a second input signal having a logic value different from that of the first input signal. The device further includes a third transistor and a fourth transistor. A first terminal of the third transistor is coupled to a second output terminal, different from the first output terminal, of the level shifter to receive a second output signal and a gate terminal of the third transistor receives the second input signal. The first output signal and the second output signal have logic values different from each other. The first to fourth terminals of the selector are different from each other.

Also disclosed is a method that includes the operation below: in response to a first input signal having a first logic level, generating, by a level shifter, a first output signal at a first output terminal of the level shifter; in response to the first input signal having a second logic level, generating, by the level shifter, a second output signal at a second output terminal of the level shifter; receiving, by a selector, the first output signal at a first input terminal of the selector and the second output signal at a second input terminal of the selector; and selecting, by the selector, the first output signal or the second output signal as a selected signal to be output to an output stage in response to the first input signal received at both of a third input terminal of the selector and a fourth input terminal of the selector.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A device, comprising: a first transistor and a second transistor, wherein first terminals of the first and second transistors are coupled to an output terminal, and gate terminals of the first and second transistors are configured to receive a first input signal; and a first current limiter, wherein a first terminal of the first current limiter is coupled to a second terminal of the first transistor to output a first output signal, and a second terminal of the first current limiter is coupled to a second terminal of the second transistor to output a second output signal; wherein a third output signal at the output terminal has a logic value different from that of the first input signal.
 2. The device of claim 1, wherein the first current limiter comprises: a third transistor having a first terminal as the first terminal of the first current limiter and a second terminal as the second terminal of the first current limiter; wherein the first output signal and the second output signal have a different logic value.
 3. The device of claim 2, further comprising: a fourth transistor coupled between the first terminal of the first current limiter and a first voltage terminal, and configured to transmit a first current to the first current limiter; a fifth transistor coupled between the second terminal of the first current limiter and a second voltage terminal different from the first voltage terminal, and configured to transmit a second current associated with the first current to the second voltage terminal in response to the first input signal; a second current limiter having a control terminal coupled to a gate terminal of the fourth transistor; a sixth transistor coupled between the first voltage terminal and a first terminal of the second current limiter, and configured to transmit a third current in response to a signal received at the second terminal of the first current limiter; and a seventh transistor coupled between a second terminal of the second current limiter and the second voltage terminal, wherein a gate terminal of the seventh transistor is configured to receive a second input signal inverted from the first input signal.
 4. The device of claim 1, further comprising: a third transistor coupled between the first terminal of the first current limiter and a first voltage terminal providing a first supply voltage; a fourth transistor coupled between the second terminal of the first current limiter and a second voltage terminal different from the first voltage terminal, wherein a gate terminal of the fourth transistor is configured to receive the first input signal; a fifth transistor having a first terminal and a gate terminal that are coupled to a gate terminal of the third transistor; an input signal generator configured to operate with a second supply voltage to generate a second input signal inverted from the first input signal; and a sixth transistor coupled between the first terminal of the fifth transistor and the second voltage terminal, wherein a gate terminal of the sixth transistor is configured to receive the second input signal; wherein the first supply voltage and the second supply voltage have different voltage levels.
 5. The device of claim 1, further comprising: a third transistor coupled between the first terminal of the first current limiter and a first voltage terminal; a fourth transistor coupled to the second terminal of the first current limiter, wherein a gate terminal of the fourth transistor is configured to receive the first input signal; and a fifth transistor coupled between the fourth transistor and a second voltage terminal different from the first voltage terminal, and configured to transmit a current received from the fourth transistor to the second voltage terminal in response to an enable signal received at a gate terminal of the fifth transistor.
 6. The device of claim 1, further comprising: a third transistor having a first terminal coupled to a first voltage terminal providing a first supply voltage; and a fourth transistor coupled between a second terminal of the third transistor and the first terminal of the first current limiter; wherein the third transistor is configured to be turned on, in response to an enable signal received at a gate terminal of the third transistor, to transmit the first supply voltage to the fourth transistor.
 7. The device of claim 6, further comprising: a fifth transistor having a first terminal coupled to the second terminal of the third transistor and a gate terminal coupled to the second terminal of the first current limiter; a second current limiter having a control terminal coupled to a gate terminal of the fourth transistor and a first terminal coupled to a second terminal of the fifth transistor; and a sixth transistor coupled between a second terminal of the second current limiter and a second voltage terminal.
 8. The device of claim 1, further comprising: an output stage configured to adjust a voltage swing of the third output signal.
 9. The device of claim 1, further comprising: a third transistor coupled between the first terminal of the first current limiter and a first voltage terminal; and a fourth transistor having a first terminal coupled to a gate of the third transistor, a second terminal coupled a second voltage terminal different from the first voltage terminal, and a gate terminal configured to receive a second input signal; wherein the second input signal and one of the first output signal and the second output signal have different logic values.
 10. A device, comprising: a level shifter, comprising a first transistor and a second transistor, wherein a gate terminal of the first transistor is configured to receive a first input signal, and a gate terminal of the second transistor is configured to receive a second input signal having a logic value different from that of the first input signal; a third transistor having a first terminal coupled to a first output terminal of the level shifter to receive a first output signal and a gate terminal to receive the second input signal; and a fourth transistor having a first terminal coupled to a second output terminal, different from the first output terminal, of the level shifter to receive a second output signal and a gate terminal configured to receive the second input signal; wherein the first output signal and the second output signal have logic values different from each other.
 11. The device of claim 10, wherein a second terminal of the third transistor is coupled to a second terminal of the fourth transistor.
 12. The device of claim 10, wherein a second terminal of the third transistor and a second terminal of the fourth transistor are coupled together at an output node configured to output a third output signal; wherein a logic value of the third output signal is different from at least one of the first and second output signals.
 13. The device of claim 10, wherein the level shifter further comprises: a fifth transistor coupled between the first and second output terminals of the level shifter, and configured to provide a threshold voltage between the first and second output terminals of the level shifter in order to enable the level shifter.
 14. The device of claim 10, further comprising: a first inverter configured to generate the first input signal according to the second input signal; and a second inverter coupled to a second terminal of the third transistor and a second terminal of the fourth transistor, and configured to invert the first output signal or the second output signal to generate a third output signal.
 15. The device of claim 10, further comprising: a fifth transistor coupled between a supply voltage terminal and second terminals of the first and second transistors, wherein a gate terminal of the fifth transistor is configured to receive an enable signal in order to enable the level shifter.
 16. The device of claim 10, further comprising: an output stage coupled to second terminals of the third and fourth transistors, and configured to generate a third output signal, wherein a logic value of the third output signal is the same as, in response to the second input signal, a logic value of the first output signal or of the second output signal.
 17. A method, comprising: in response to a first input signal having a first logic level, generating, by a level shifter, a first output signal at a first output terminal of the level shifter; in response to the first input signal having a second logic level, generating, by the level shifter, a second output signal at a second output terminal of the level shifter; receiving, by a selector, the first output signal at a first input terminal of the selector and the second output signal at a second input terminal of the selector; and selecting, by the selector, the first output signal or the second output signal as a selected signal to be output to an output stage in response to the first input signal received at both of a third input terminal of the selector and a fourth input terminal of the selector, wherein the first to fourth terminals of the selector are different from each other.
 18. The method of claim 17, further comprising: controlling, by a second input signal inverted from the first input signal, the level shifter to generate a current flowing between the first and second output terminals of the level shifter.
 19. The method of claim 17, wherein the selected signal and one of the first and second output signals have different logic values.
 20. The method of claim 17, wherein the third input terminal of the selector is a gate terminal of a first transistor in the selector, and the fourth input terminal of the selector is a gate terminal of a second transistor in the selector. 